Changes to the design of the top of One World Trade Center have raised questions about the ultimate height of the tower, which is currently planned as the tallest building in North America.

As first reported by the New York Times, the Durst Organization has removed the cladding for the structure on top of the tower, which may change the calculation of the building’s ultimate height. Based on preliminary information, it is unclear whether the remaining structure will be included in the final measurement, which could cut several hundred feet off the building’s official architectural height.

The result was a wave of articles and calls to the CTBUH, which is widely regarded as the arbiter of height measurements and the lists of tallest buildings in the world. The Wall Street Journal, New York Post, New York Daily News and Associated Press covered the story.

We are aware that changes have been announced to the design of the structure on top of One World Trade Center, which may affect the final height measurement for the building. We understand that sculptural cladding has been removed, which will change the structure.

One World Trade Center, which is still under construction, is currently listed in the CTBUH’s Skyscraper Center at an anticipated height to “architectural top” of 1,776 feet. This includes the structure described in the materials previously provided by the architect as a spire. A spire is typically a permanent structure and part of the architecture and artistic expression of the building.

The CTBUH includes spires in its height measurement to “architectural top,” the primary category in ranking the tallest buildings in the world. But antennas, masts, water towers and other functional-technical structures – which often are not designed by the architect of the building and change according to prevalent technologies – are not included in the height measurement to the architectural top. However, they are included in measurements to the architectural “tip,” a secondary category tracked by the CTBUH. Definitions can be found on the CTBUH website at www.CTBUH.org.

At this point, since the building is far from completion, there is no final determination on the height of One World Trade Center. A final determination will be made by the CTBUH Technical Height Committee based on analysis of the drawings and other information submitted by the building owner, development and consultant team. Building designs often change during construction and final ratification of the height and formal recognition on the list of 100 Tallest Completed Building in the World occur after the building is officially completed and application details submitted.

Over 40 years the CTBUH has developed detailed criteria for measuring the height of buildings, which are internationally recognized in the industry. Any disputes are resolved by the CTBUH Height Committee - a panel of industry experts specifically set up for this purpose.

For more data on One World Trade Center and thousands of tall buildings around the world, including tallest rankings, visit The Skyscraper Center (www.skyscrapercenter.com)